A major goal of my career as a physician-scientist is to understand the mechanisms of inherited neurodegenerative diseases, with the ultimate aim of developing therapies. Charcot-Marie-Tooth (CMT) disease is the most common inherited peripheral neuropathy, affecting one in 2,500 individuals worldwide. To date, six aminoacyl-tRNA synthetase (ARS) genes have been implicated in CMT disease with an axonal pathology. Twenty-one mutations at five ARS loci have been identified in patients with autosomal dominant, axonal CMT type 2 (CMT2) disease. To date, the majority of disease-associated ARS alleles cause a loss of function by either interfering with the catalytic activity or mislocalizingthe enzyme in neurons. This indicates that impaired ARS function is an important aspect of CMT2 disease. Interestingly, the majority of CMT- associated ARS mutations are missense changes; frameshift and nonsense mutations have not been identified in dominantly inherited CMT2 disease. These observations led to our hypothesis that a dominant-negative effect may be responsible for the axonal phenotype; however, a dominant-negative mechanism has not been evaluated. Endogenous glycyl-tRNA synthetase (GARS) forms discrete puncta in cells, including in the axons of human peripheral nerves. Seven of the 12 GARS mutations associated with CMT disease prevent the formation of puncta in vitro, indicating that these puncta may be important for the health and maintenance of axons. However, the composition and function of the puncta are unknown. We hypothesize that GARS associates with components of the translational machinery in these puncta to promote efficient protein translation within axons. To address these critical issues, we will: (1) directly evaluate GARS mutations for a dominant-negative effect in vivo; and (2) characterize the function of GARS puncta in axons. These experiments will improve our understanding of GARS-related CMT disease and will inform therapeutic development. Importantly, this project will allow me to develop the skill set necessary for a research career focused on understanding the mechanisms of neurodegenerative diseases.